As to a method for polymerization of olefin using a transition metal compound as a catalyst for olefin polymerization, U.S. Pat. No. 4,894,424 discloses a method for producing an ethylene polymer and copolymer using a transition metal compound in which the transition metal has an oxidation number of 3 in Group IV of the Periodic table. The catalyst is produced by, as shown in Reaction Scheme 1, reduction of a transition metal compound in which the transition metal has an oxidation number of at least 4 in Groups IV, V or VI of the Periodic table, for example, a titanium compound having a general formula of Ti(OR)mCln, with a Grignard compound having a formula of RMgCl which is obtained from magnesium (Mg) and an alkyl chloride (RCl).

wherein, R represents C1-C6 alkyl; X represents a halogen atom; and m+n=4.
Since the catalyst is produced by reduction with a Grignard compound, 80% or more of titanium metal included in the catalyst exist in the from of Ti3+, i.e. having an oxidation number of 3.
Recently, many attempts to make use of aryloxy ligand in a non-metallocene catalyst have been reported. As an example, a catalyst for olefin polymerization using a compound in which 1,1′-bi-2,2′-naphthoxy ligand is bound to a transition metal such as titanium or zirconium and derivatives thereof, is disclosed in p. 3008, vol. 117 of J. Am. Chem. Soc.; and a chelated catalyst for olefin polymerization which is produced by substituting a halide ligand in titanium and zirconium halide compound with a chelated phenoxy group, thereby being capable of producing a polymer having high molecular weight with a narrow molecular weight distribution, is disclosed in Japanese laid-open No. 340711 (Heisei-6) and EP Patent No. 0606125 A2; and a catalyst for ethylene polymerization using a titanium compound having a bisphenolato ligand as a main catalyst and methylaluminoxane (hereinafter, referred as MAO) as a co-catalyst, is disclosed in p. 5069, vol. 15 and p. 1562, vol. 30 of Macromolecules. 
However, those conventional non-metallocene chelated catalysts for olefin polymerization using titanium and zirconium compounds as described above disadvantageously require the use of expensive MAO or boron compound as a co-catalyst, and they are not easily either produced or modified, due to their structure in which two aryloxy groups are linked to each other.